1. Department of Biology and Center for Molecular Genetics, University of California at San Diego, La Jolla, California 92093-0347, USA
2. National Institutes of Health, NICHD, 18 Library Drive, Bethesda, Maryland 20892-5430, USA
3. Cold Spring Harbor Laboratory, P.O. Box 100, Cold Spring Harbor, New York 11724, USA
4. Present address: Department of Biochemistry, University of Washington, Seattle, Washington 98195, USA

Correspondence to: Jessica K. Tyler¹ Correspondence and requests for materials should be addressed to J.T.K. (e-mail: Email: jkadonaga@ucsd.edu). The GenBank accession number for the dASF1 cDNA is AF189278.

Chromatin assembly is a fundamental biological process that is essential for the replication and maintenance of the eukaryotic genome^{1, 2, 3, 4}. In dividing cells, newly synthesized DNA is rapidly assembled into chromatin by the deposition of a tetramer of the histone proteins H3 and H4, followed by the deposition of two dimers of histones H2A and H2B to complete the nucleosome—the fundamental repeating unit of chromatin⁵. Here we describe the identification, purification, cloning, and characterization of replication-coupling assembly factor (RCAF), a novel protein complex that facilitates the assembly of nucleosomes onto newly replicated DNA in vitro. RCAF comprises the Drosophila homologue of anti-silencing function 1 protein ASF1⁶ and histones H3 and H4. The specific acetylation pattern of H3 and H4 in RCAF is identical to that of newly synthesized histones. Genetic analyses in Saccharomyces cerevisiae demonstrate that ASF1 is essential for normal cell cycle progression, and suggest that RCAF mediates chromatin assembly after DNA replication and the repair of double-strand DNA damage in vivo.